Skip to content

C
clone-Linux

gsplhtlxg / clone-Linux

通知 2
Star 0
Fork 1
C
clone-Linux

体验新版 GitCode，发现更多精彩内容 >>

切换分支/标签
  1. 14 8月, 2017 2 次提交
  3. 02 8月, 2017 27 次提交
  5. 16 7月, 2017 1 次提交
  7. 01 7月, 2017 1 次提交
  9. 27 6月, 2017 1 次提交
    • L
      x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF · f8475cef
      由 Len Brown 提交于 
      The goal of this change is to give users a uniform and meaningful
result when they read /sys/...cpufreq/scaling_cur_freq
on modern x86 hardware, as compared to what they get today.

Modern x86 processors include the hardware needed
to accurately calculate frequency over an interval --
APERF, MPERF, and the TSC.

Here we provide an x86 routine to make this calculation
on supported hardware, and use it in preference to any
driver driver-specific cpufreq_driver.get() routine.

MHz is computed like so:

MHz = base_MHz * delta_APERF / delta_MPERF

MHz is the average frequency of the busy processor
over a measurement interval.  The interval is
defined to be the time between successive invocations
of aperfmperf_khz_on_cpu(), which are expected to to
happen on-demand when users read sysfs attribute
cpufreq/scaling_cur_freq.

As with previous methods of calculating MHz,
idle time is excluded.

base_MHz above is from TSC calibration global "cpu_khz".

This x86 native method to calculate MHz returns a meaningful result
no matter if P-states are controlled by hardware or firmware
and/or if the Linux cpufreq sub-system is or is-not installed.

When this routine is invoked more frequently, the measurement
interval becomes shorter.  However, the code limits re-computation
to 10ms intervals so that average frequency remains meaningful.

Discerning users are encouraged to take advantage of
the turbostat(8) utility, which can gracefully handle
concurrent measurement intervals of arbitrary length.
Signed-off-by: NLen Brown <len.brown@intel.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
      f8475cef
  11. 26 6月, 2017 2 次提交
  13. 24 6月, 2017 1 次提交
    • L
      x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" · 51204e06
      由 Len Brown 提交于 
      cpufreq_quick_get() allows cpufreq drivers to over-ride cpu_khz
that is otherwise reported in x86 /proc/cpuinfo "cpu MHz".

There are four problems with this scheme,
any of them is sufficient justification to delete it.

 1. Depending on which cpufreq driver is loaded, the behavior
    of this field is different.

 2. Distros complain that they have to explain to users
    why and how this field changes.  Distros have requested a constant.

 3. The two major providers of this information, acpi_cpufreq
    and intel_pstate, both "get it wrong" in different ways.

    acpi_cpufreq lies to the user by telling them that
    they are running at whatever frequency was last
    requested by software.

    intel_pstate lies to the user by telling them that
    they are running at the average frequency computed
    over an undefined measurement.  But an average computed
    over an undefined interval, is itself, undefined...

 4. On modern processors, user space utilities, such as
    turbostat(1), are more accurate and more precise, while
    supporing concurrent measurement over arbitrary intervals.

Users who have been consulting /proc/cpuinfo to
track changing CPU frequency will be dissapointed that
it no longer wiggles -- perhaps being unaware of the
limitations of the information they have been consuming.

Yes, they can change their scripts to look in sysfs
cpufreq/scaling_cur_frequency.  Here they will find the same
data of dubious quality here removed from /proc/cpuinfo.
The value in sysfs will be addressed in a subsequent patch
to address issues 1-3, above.

Issue 4 will remain -- users that really care about
accurate frequency information should not be using either
proc or sysfs kernel interfaces.
They should be using using turbostat(8), or a similar
purpose-built analysis tool.
Signed-off-by: NLen Brown <len.brown@intel.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
      51204e06
  15. 22 6月, 2017 2 次提交
  17. 21 6月, 2017 1 次提交
  19. 20 6月, 2017 2 次提交